Television system



Dec. 21, 1943. T. T. EATON TELEVISION SYSTEM Filed Dec. 51, 1940 v IIMPLIF'IEI? l/IDED SIGN/9i INPUT wzwo ture.

system.

UNITED STATES. PATENT OFFlCiJ f g a I 2,337,234

Thomas '1'. Batch, mason Heights, N. J... w l or to Radio Corporation of America, a corporation of Delaware Application December 31, 1940, Serial No. 372,471 3' Claims. '(cl. via-7.2)

This invention relates to television systems and more particularly to direct current voltage reinsertion to control the background of television August 1937, there is produced at the output of the pickup device a train of signals representatelevised without the necessary direct current voltage component indicating whether the range of contrast is taken from a bright or, dull pic- Under these conditions, the train of the picture signals representing a bright image will be similar to a train ofsignals representing a dull image having the same contrast as that of the bright image.

' It is customary in the television art to reinsert the direct current voltage component which has been suppressed during transmission, as for example, where it is suppressed in the associated alternating current amplifier. These direct current voltage reinsertion circuitsdepend for their operation upon the transmission of periodically recurring control pulses which are caused togo to a fixed voltage level such as 'black in a pic-- ture. Such recurring pulses usuallyare the synchronizing pulses.

of the video signal channel. Furthermore, a

' manual control means completely independent tiveof the range of contrast of the picture being of the automatic control means is provided, whereby there is an independent 'manual and automatic control to maintain a reference in the train of picture signals depending upon the average brightness of the televised object.

The primary object of this invention is to improve the image representation of a transmitted video signal.

Another'object of this invention is to provide a video signal with a reference component whereby the transmitted signal is representative of the average brilliance of the televised object.

Still another object of the invention is to provide an improved automatic and manual background control.

Other and incidental objects of this invention will be apparent to those skilled in the art from the following specification considered in connection with the accompanying drawing, in

. which When, however, it is desired to reestablish the 7 reference level to control the brightness of the image, which reference information the television pickup tube does not convey, it is necessary to control the amount of reinserted direct current voltage in accordance with the average brightnessof the televised object.

Bedford Patent 2,192,121, patented February 27, 1940, shows and describes one system and methodfor reestablishing the desired background control direct current voltage component. It very often becomes desirable to manually control the background independently of auto matic control furnished by the average-illumination of the scene'being televised. Furthermore, it is desirable that both manual and auto matic control function at the same point in the According to this inventiomthere is provided a light sensitive device adapted to produce a voltage dependent upon the average brightness of the object being televised and cause this volt of the image on the film 3.

Figure 1 is a block and circuit diagram showing a television transmission system utilizing one formof this invention;

Figure 2 is a circuit diagram showing another form of this invention; and

Figure 3 is a circuit diagram showing still another form of this invention.

Referring now in'more detail to Fig. 1, there is shown a pickup camera I which maybe of the type such as described "by Iams and Rose in an article entitled Television pickup tubes with cathode ray beam scanning," published in the Proceedings of the I. R. E., August 1937, which supplies a train ofpicture signals representative of the image on the film 3 under scansion to an amplifier 5 which, in turn, supplies the amplified video signal to the control electrode 1 of an amplifier tube 9 through coupling-condenser II.

A light sensitive device 13 is mounted adjacent the film 3 in order to collect light from a source I! through the film 3 whereby there will be pro-' duced a control signal from the light sensitive device representative of the average brightness plied to the control electrode ll of the tube 10 through a potentiometer 2| which is provided as 'a manual adjustment of the amount of control signal required. A bias supply voltage for the light sensitive device 13 is. supplied through the potentiometer 23 which is'connected to any suitable power source.

age to control a clipper tube in the amplifier 66 The tube is also includes a cathode 21 an anode 23. The cathode circuit includes a re- This signal is ap-- element of the television camera I.

. trode I is connected in series with a control electrode resistor 35 which is in turn connected to the variable tap of a potentiometer 31 which serves to manually control the bias potential on the control electrode 1. The output circuit of the tube 9 includes the anode 39 which is connected to the transmitter 4| through a coupling condenser 43. The anode 39 is supplied with a positive potential through the anode resistor 45 and a series peaking coil 41.

The operation of the circuit will now be more fully described. As a motion picture film 3 passes through the projection apparatus, an image thereof is projected on the light sensitive mosaic This produces charges upon the element (in a well known manner) and by scanning the element a train I of picture video signals representative of the optical image may be developed. These signals are then amplified in the amplifier 5 and applied to the control electrode of the clipper tube 9.

The average film brightness responsive system including the light source l5 and the light responsive device I3 is located at such a position that the average brightness of the image being televised from the film 3 will produce in the average light responsive circuit a signal whose amplitude is dependent upon the average brightness of an adjacent image or the same section of the'film 3 being televised. The film preferably moves' in the direction 0! the arrow so that the control signal produced will anticipate the corresponding picture signal train by a small amount equal to the time it takes the film to move from the control gate to the picture gate. This allows the time delayed control circuit to be ready 'i'or the picture. signal. This control voltage is applied to the control electrode I! of the tube l9 in such a polarity that; when the imag being televised from the film 3' is bright a less positive voltage is applied to the control electrode l9. A less positive voltage on the control electrode II will cause the cathode follower 22 to 80 less positive whereby the connection between the cathode 22 and the cathode 29 causes the cathode 29 also to go less positive.

When the cathode 29 goes less positive it causes a greater average current to fiow through the amplifying tube 9 and thus establishing a-greater output signal for a bright picture which necessarily results in a reestablishment or thereierence voltage in the picture signal which is lost by the pickup camera I. I

It follows that when there is a dull or less bright image on the film 3 the control electrode ll goes more positive whereby the cathode 101- lower 22 goes more positive and causes the cathode 29 also to go more positive whereby the difierential between the cathode 29 and the control electrode '1 is increased thus allowing less current to flow through the amplifier tube 9 which results in a signal having a lower average amplitude than in the case of a bright image.

The bias on the control-electrode I may be in-- dependently controlled by manually varying the adjustment of the potentiometer 31. By providing the manual adjustmentin the control electrode circuit of the tube 9 this adjustment may be changed without in any way electing the automatic adjustment which is maintained through the cathode circuit of the tube 9.

The change in the adjustment of the potentiometer 31 in no way afiects the incoming video signals from the amplifier 5.

Fig. 2 shows another form of this invention wherein like numerals refer to similar parts. The light sensitive device I3 is supplied with its polarizing potential through a relatively large resistance including resistances 25, 21 and 49 which is included in the cathode circuit of the tube l9. A resistance Si is connected to a source of positive potential and to the junction between resistances 25 and 49 and to the resistance 2i. It therefore follows that the potential drop across the resistances 49 and 21 caused by the positive potential applied thereto through resistance BI is also applied to the photocell I3 through the resistance 2 I.

This, however, has no effect upon the functioning of the control circuit because the control potential from the cathode 22 of the tube I9 is applied to the control electrode 29 of the tube 9. It is desirable to maintain this potential somewhat above the saturation of the light sensitive device I 3 so that no fluctuation in potential applied thereto will cause a change in the sensitiveness of the light responsive device l3.

Fig. 3 shows another form of this invention in which an additional amplified tube is included in the circuit to provide flexible adjustment and general overall stabilization. There is furthermore provided still another method of obtaining polarizing potential for the light sensitive device l3. A resistance 53 is provided in the cathode circuit of the tube 55 to stabilize the amplifier circuit by degeneration and also to supply bias to tube 55. A potentiometer 56 is shunted with a voltage source to supply bias potential to the control electrode 59. The output signal from the tube 55 is applied to the control electrode [1 of the tube l9 which functions in this form of the invention in a manner similar to that previously described.

It will be noted that a direct current amplification connection is made between the output of tube 55 and tube 11 in order to pass the lower 'irequency necessary for the proper functioning of this control circuit. v

In this form ofv the invention the tube 9 is supplied with the video signal in a similar manner as that shown and described in Fig. 1. The

manual control is obtained throu h the variaor the automatic control which may or may not be utilized at the discretion of the operator.

While several systems for carrying thi invention into effect have been indicated and described, it will be apparent to on skilled in the art that this invention is by no mean limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of this invention as set forth in the appended claims.

I claim as my invention: 1. In a television transmitting, system, a. scanning device for developing picture signals, an

amplifier for said picture signals including an amplifying tube having acathode, a control electween said cathode and a point of fixed potential,

trode and an anode, means including a light,

responsive device for developing a signal wave whose amplitude variesin accordancewith occurring variations in overall brilliancy of the object-being'scanned, means for applying said picture vsignal between said control electrode and a point of fixed potential, meansfor applying said signal wave between said cathode and said ,and means for manually varying the bias potential on said control electrode independently of the potential of said cathode.

point of fixed potential to automatically control v the conductance of said amplifying tub in accordance with occurring variations in the over- I all brilliancy of said object, and meansto' manually control the bias potential between said control electrode and said point of fixed potential independently of said automatic control.

2. In a television signal transmitting system including a scanning device for developing picture signals representative of an object being scanned, and an amplifier for said picture si nals including an amplifying tube having a cathode, a control electrode and an anode, means for providing background control of the transmitted image including means for developing a signal wave whose amplitude varies in accordance with occurring variations in overall brilliancy of said 3. In a television signal transmitting system including a scanning device for developing picture signals representative ofan object being scanned and an amplifier for said picture signals including an amplifying tube having a cathode, a control electrode and an anode, means for providing background control of the transmitted image comprising, in combination, a manual control for varying the bias potential on said control electrode, a light sensitive device for developing a control signal whose amplitude varies in accordance with occurring variations in overall brilliancy of said object, a control tube havin a cathode and an input circuit including said light responsive. device, a cathode resistor connected to a point of fixed potential and common to said amplifying tube and said control tube cathodes vto transmit said control signal to said amplifying tube independently of said picture signal and said manual control of the bias of said amplifyingtube.

' THOMAS T. EATON. 

